Advancements in communication technologies have permitted the introduction, and popularization, of new types of communication systems. As a result of such advancements, the rate of data transmission and the corresponding amount of data permitted to be communicated in such communication systems, has increased relative to existing types of communication systems.
A radio communication system is representative of a type of communication system which has benefited from advancements in communication technologies. Because radio-links are utilized to form communication channels in a radio communication system, increased communication mobility relative to conventional wireline communication systems is generally possible.
Bandwidth limitations, however, sometimes limit the communication capacity of the radio communication system. That is to say, generally, only a limited amount of the electromagnetic spectrum is allocated to usage by a particular radio communication system. When the communication capacity is limited by the bandwidth allocated to the radio communication system, an increase in communication capacity requires more efficient utilization of the allocated bandwidth.
Use of digital communication techniques, for instance, provides a manner by which to increase the bandwidth efficiency of communications in a communication system. The use of such digital techniques is particularly advantageously utilized in a radio communication system due to the particular need to efficiently utilize the bandwidth allocated in such a system.
Typically, when utilizing digital communication techniques, information which is to be communicated is digitized to form digital bits. In one technique, the digitized bits are formatted into sequences which form packets of which one or more packets sometimes together form a frame. The terms packet and frame shall be, at times, used interchangeably herein to refer to data which is to be communicated. Because the sequences of the data forming the packets or frames can be communicated at discrete intervals and thereafter concatenated together to recreate the informational content of the data.
Because packets or frames of data can be communicated at discrete intervals, a frequency band need not be dedicated solely for the communication of data generated by one sending station or transmission to one receiving station as conventionally required in analog communications. Instead, the frequency band can be shared amongst a plurality of different sending and receiving station-pairs. Because the same frequency band can be utilized to effectuate communications by the plurality of pairs of communication stations, improved communication capacity is possible.
Packet data communications are effectuated, for instance, in conventional LANs (local area networks). Wireless networks, operable in manners analogous to wired LANs, referred to as WLANs (wireless local area networks) have also been developed and are utilized to communicate data over a radio-link.
The IEEE (Institute of Electrical and Electronic Engineers) 802.11 specification sets forth, inter alia, the standards of operation of an exemplary WLAN. The system set forth in the standard provides for multi-user communications. Data is formatted into frames and sent over a radio-link. Once received, an acknowledgment indication is returned to indicate reception of the frame.
The IEEE 802.11 standard, as presently-promulgated, defines a contention period (CP) and a contention free period (CFP). The contention period defines a random access period during which any sending station is permitted random access to communicate a frame of data. And, the contention free period data is permitted to be communicated responsive to a polling procedure in which allocations are made as to when a sending station is permitted to communicate a frame of data.
Conventionally, subsequent to reception of a frame of data, an acknowledgment indication is returned to the sending station from which the frame is sent. A manner is set forth by which an acknowledgment indication to a frame of data is returned during transmission of a subsequent frame of data. The acknowledgment indication is said to “piggy-back” upon the subsequent frame of data. Through such a process, the overhead otherwise required to generate acknowledgment control frames is obviated.
When each frame of data is transmitted at the same transmission rate, the acknowledgment indications are returned at the same transmission rate at which the initially-transmitted frame was transmitted. However, the system set forth in the IEEE 802.11 standard provides for multi-rate communications. That is to say, separate communication sessions within a single contention free period are able to be effectuated at different transmission rates. The transmission rates at which a communication session is effectuated, is dependent, for instance, upon hardware capabilities of the mobile terminal involved in the communication session communication channel characteristics, or other considerations.
A problem occurs, though, when the acknowledgment indication responsive to a frame of data is sent at a higher transmission rate than that at which a mobile terminal is operable. That is to say, when a sending station operable to transmit and to receive at a relatively low transmission rate receives an acknowledgment indication transmitted at a high transmission rate, detection of the acknowledgment indication might be missed.
Therefore, a manner by which better to assure that an acknowledgment indication is detectable in a multi-user, multi-rate communication scheme is needed.
It is in light of this background information related to multi-rate, multi-user communication systems that the significant improvements of the present invention have evolved.